1. Field of the Invention
The present invention relates to a folded sheet pressing device which enhances a folded edge of a sheet subjected to a folding process, and a sheet processing apparatus and an image forming apparatus which include the folded sheet pressing device.
2. Description of the Related Art
In image forming apparatuses such as copying machines, printers, facsimiles, or multi-function peripherals, an image forming apparatus has been provided which includes a sheet folding device capable of performing, for example, Z-folding, two-face folding, inward three-face folding, outward three-face folding, simple four-face folding, and side-by-side four-face folding on a sheet such as a sheet having an image formed thereon. Further, as such a sheet folding device, there is known a sheet folding device which includes a folded sheet pressing device configured to enhance the folded edge of the sheet folded by a folding member.
Although a pressure is applied to the sheet when the folded edge of the sheet is enhanced by the folded sheet pressing device, if a flexure is present in the sheet at this time, the flexure is crushed by the pressure, so that it becomes a wrinkle. As a result, a problem arises in that the quality of the sheet subjected to the folding process is degraded.
Therefore, in the sheet folding device disclosed in, for example, Japanese Patent Application Laid-open No. 2009-208849, the sheet or the sheet bundle which has passed through the folding process is temporarily stopped to allow folded sheet pressing rollers to move thereon along the folded edge while pressing the sheet or the sheet bundle. This process prevents occurrence of an unnecessary flexure, and hence prevents generation of the wrinkles.
However, in the sheet folding device disclosed in Japanese Patent Application Laid-open No. 2009-208849, since the folded sheet pressing process is performed with a temporal halt of the sheet or the sheet bundle, a problem arises in that the folding productivity is degraded.
Therefore, there is a need of a folded sheet pressing device capable of performing the folded sheet pressing process without degrading the sheet folding productivity and generating the wrinkle in the sheet, and a sheet processing apparatus and an image forming apparatus which include the folded sheet pressing device.